In recent years, plastics and plastic composites have become increasingly important materials for making various types of articles. These thermoplastic-containing materials have begun replacing metals as structural members. Such thermoplastic materials offer outstanding mechanical properties, unique flexibility and design capabilities, and ease of fabrication. Additional advantages include their light weight, corrosion resistance, and affordable price. In fact, high-strength and light-weight thermoplastic composite materials are strongly demanded for various engineering applications. Such applications have included the use of thermoplastic composites in construction materials, flooring materials, and in fabricating furniture.
Recently, attention has turned to the possibility of manufacturing plastics with desirable mechanical properties by reinforcing the plastics with fibers. Such reinforcement adds strength to the composites without adding much weight. These fiber-reinforced structures exhibit excellent strength when molded into articles of manufacture like those discussed above.
In addition to the increasing demand for such fiber-reinforced thermoplastic composites to replace conventional structural materials, the shortage of facilities for disposing of solid wastes is rapidly growing. The largest portion of the wastes in the solid waste stream consists of paper and other cellulosic fibers, including textiles and wood. Plastics make up another large portion of the wastes. Among the cellulosic fiber wastes, a large portion of the fiber is discarded printed material, including newspapers. Of the remaining cellulosic fiber waste and plastics waste, a large portion consists of packaging materials. Many of these packaging materials, like the printed cellulosic materials, have ink printed thereon for advertising or other identification purposes. Accordingly, a very large portion of the solid waste stream consists of cellulosic fibers and plastics.
One prior art composite material, as shown in U.S. Pat. No. 3,956,541 to Pringle, uses particulate wood filler materials such as wood chips, comminuted paper and sawdust to reinforce a composite made from thermoplastic insulation found in scrap electrical wire and cables. The filler materials are held together with the thermoplastics by adding a phenolic resin binder such as urea-formaldehyde.
British Patent No. 1,369,204 issued to Paske shows a method of making a plastics product from a raw material having more than 85 percent by weight reclaimed synthetic thermoplastic material wherein the thermoplastic materials are compressed at pressures between 10 and 1,000 pounds per square inch (psi). The thermoplastic materials must be present in the composition at more than 85 percent by weight. The remaining 15 percent or less of the product may include small quantities of incidental constituents such as metal foil, cardboard, paper, paperboard, sawdust, and other garbage materials.
Other prior art structures, such as those disclosed in U.S. Pat. No. 4,810,445 to Lamb, Sr., et al. and U.S. Pat. No. 4,045,603 to Smith show laminated materials wherein a middle layer is formed by combining shredded 42-pound Kraft paper coated with polyethylene or other cellulose fiber products such as shredded tree bark with thermoplastics to form a thermoplastic layer having paper encapsulated therein. Such middle layers are then laminated between two paper webs in Lamb and between two hardened thermoplastic layers in Smith to ensure bonding of the cellulose particles.
U.S. Pat. No. 4,874,095 to Warych discloses package edge protectors that are not susceptible to attack by moisture. The protectors are formed under heat and pressure from paper-waste cuttings having an edge length of 2 to 5 mm and larger and low molecular weight thermoplastics. The final product results in a protector wherein the paper cuttings are encapsulated within the thermoplastic materials.
Other patents, such as U.S. Pat. No. 4,098,649 to Redker and U.S. Pat. No. 4,968,463 to Levasseur show processes for using waste stream materials, including paper, wood, and plastics. Redker discloses a process of destructively distilling organic waste material by an extruder. Levasseur discloses a process for producing extruded or molded objects formed from garbage materials including thermoplastics present in an amount of over 65 percent by weight and other garbage filler agents such as compost refuse, paper, rags, or materials extracted from other household wastes. The disclosed process requires that the water content of the waste products be less than three percent by weight.
Although the prior art shows a combination of thermoplastic materials and certain types of cellulosic materials, the particular features of the present invention are absent from the prior art. The prior art is generally deficient in affording a proper attachment between the thermoplastic resin and the cellulosic material to form a coherent member. The prior art has attempted to achieve such coherency but has had to employ specific binders, inordinate amounts of thermoplastic material, large pieces of cellulosic materials, or other materials acting as binding agents. The present invention, however, overcomes the shortcomings of the prior art in that a method is disclosed herein for forming a coherent mass of thermoplastic and cellulosic material.
A patent application directed toward an invention similar to that presently claimed is currently pending at the time this application was filed. That application, Ser. No. 07/692,004, filed on Apr. 26, 1991 by an inventive entity including the presently named inventor, is directed to a fiber-reinforced thermoplastic composition and molded composite articles made therefrom. The invention therein, however, is directed to cellulosic fiber-reinforced thermoplastic compositions wherein cellulosic fibers generally have a moisture content of from about 5 to about 7 percent by weight. That application is incorporated herein in its entirety by reference thereto.